Welcome to video games.
The problem with real life dimensions is they do not look correct through a first person screen perspective that FPS games use. Railings and walls at realistic heights look too low and doors, stairs, and windows look too small.
I really wish this wasn't the case but it is, and it's a nightmare to solve... you basically have to trade off. Do you want a playable area with space to move that is much larger than real life or do you want a cramped space which is frustrating to navigate which has realistic dimensions?